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Thread: hood vent ideas

  1. #1
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    hood vent ideas

    Hello all,
    I am looking into doing hood vents for my car. I have a spare hood that contacted my windshield and bent at the attachment point. I would like to put some hood vents into it and use it when I am on the track to try and help keep the car cooler. I would like to see some peoples ideas on how to do this in a cheaper way. I know of the GTR style hood vents, but at over 100 dollars, it is a pricey on a bent hood. Please post pictures of what you have done or what you have seen.

    Thanks

    Michael

  2. #2
    mslevin's Avatar
    mslevin is offline Have you checked RealOEM? BMW CCA Member
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    For my Jeep, I used floor vents from Home Depot. They were $2-3 each, and I just painted them black.



    Not the prettiest, but they reduced engine temps by 10-15deg while on the trail. If you're looking for a cheap solution, doesn't get much better than this.

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    I was thinking of doing that, I was just hoping for something that I haven't thought of yet. That is probably my best option.

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    I picked up a hood vent from a Ford Shelby GT500 for my project car:





    Nice design and only $50 or so from Ford Performance Parts.
    Attached Images Attached Images

    Emre (OO=[][]=OO) 318is

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    I have read the extractor vent right after the radiator is the best place.

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    Quote Originally Posted by Emre View Post
    I picked up a hood vent from a Ford Shelby GT500 for my project car:





    Nice design and only $50 or so from Ford Performance Parts.

    I have heard of people using the mustang vent. I have also heard people needing to modify the mustang vent to fit on an E36. The vent is to long to fit on the BMW hood nicely.

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    MKAH Motorsports Hood Vents


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    Quote Originally Posted by pbonsalb View Post
    I have read the extractor vent right after the radiator is the best place.
    looking at it from external airflow standpoint this might be true. I look at it from the internal airflow standpoint as well.
    At the track the engine bay is being inflated with air thru the front grill. This air needs to be evacuated in order to cool the engine-bay. Rather than evacuating it up front only near radiator (thereby creating a more stagnant heated air trap near the firewall) I would think that by also evacuating the air further back (near the firewall) it would get rid of more hot air = cool engine more

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    Quote Originally Posted by Haifisch M3 View Post

    looking at it from external airflow standpoint this might be true. I look at it from the internal airflow standpoint as well.
    At the track the engine bay is being inflated with air thru the front grill. This air needs to be evacuated in order to cool the engine-bay. Rather than evacuating it up front only near radiator (thereby creating a more stagnant heated air trap near the firewall) I would think that by also evacuating the air further back (near the firewall) it would get rid of more hot air = cool engine more
    But you have to be mindful of negative pressure zones or else you are just stuffing more air into the engine bay. The reason that directly behind the radiator is the preferred spot is due to a low pressure zone created by the air being forced over the nosepanel. Air further behind will evacuate around the tranny tunnel and below the motor.

  10. #10
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    Quote Originally Posted by Haifisch M3 View Post
    looking at it from external airflow standpoint this might be true. I look at it from the internal airflow standpoint as well.
    At the track the engine bay is being inflated with air thru the front grill. This air needs to be evacuated in order to cool the engine-bay.
    When you're talking about engine "cooling," you're really talking about bringing down water and oil temp. Ambient air temp under the hood doesn't really matter much for engine cooling, because the amount of radiant heat lost to the engine bay is going to be insignificant compared to internal cooling by water and oil.

    The idea of putting a hood vent close to the nose of the car is to increase the efficiency of water cooling by sucking hot air away from the radiator. If you design your system properly, you can also improve oil cooling. Part of that involves building ducting to force air up through the vent. Lots of factory race and rally cars (Lancer Evolution, Chevy C6R, Peugeot 405 T16, Viper GTS-R, etc. etc.) use this arrangement.

    Quote Originally Posted by Haifisch M3 View Post
    Rather than evacuating it up front only near radiator (thereby creating a more stagnant heated air trap near the firewall) I would think that by also evacuating the air further back (near the firewall) it would get rid of more hot air = cool engine more
    Vents at the very back of the hood tend to push air down rather than pull air out. This is why most modern cars have vents in back there: to draw in fresh air (which then generally gets pushed into the cabin).

    Take a look at the Lancia Delta HF Integrale Evo II below. The front vent pulls air up through the radiatior; the rear vent pushes air down into the intake:



    Last edited by Emre; 07-29-2017 at 01:33 PM.

    Emre (OO=[][]=OO) 318is

  11. #11
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    Quote Originally Posted by olemiss540 View Post
    But you have to be mindful of negative pressure zones or else you are just stuffing more air into the engine bay. The reason that directly behind the radiator is the preferred spot is due to a low pressure zone created by the air being forced over the nosepanel. Air further behind will evacuate around the tranny tunnel and below the motor.
    correct but what causes air evacuation is pressure differential and since the engine bay has higher pressure than top of the hood it should still evacuate. Granted I have no test data to confirm my theory. The other fact to consider is that hot air rises so there should be pocket of hotter air relatively stagnant near the firewall and top of valve cover that is not affected by the flow from front grill to tranny tunnel. I have seen the test with the taped on strings...would be interesting to see strings taped to a vent near the back of the hood...

    maybe mslevin will volunteer to run that test for us


    c_3105m.jpg
    my louver vent design is shown above, works great
    wanted to add another one front center per prevailing wisdom but don't like the look as much

  12. #12
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    Quote Originally Posted by Emre View Post
    When you're talking about engine "cooling," you're really talking about bringing down water and oil temp. Ambient air temp under the hood doesn't really matter much for engine cooling, because the amount of radiant heat lost to the engine bay is going to be insignificant compared to internal cooling by water and oil.

    The idea of putting a hood vent close to the nose of the car is to increase the efficiency of water cooling by sucking hot air away from the radiator. If you design your system properly, you can also improve oil cooling. Part of that involves building ducting to force air up through the vent. Lots of factory race and rally cars (Lancer Evolution, Chevy C6R, Peugeot 405 T16, Viper GTS-R, etc. etc.) use this arrangement.

    Vents at the very back of the hood tend to push air down rather than pull air out. This is why most modern cars have vents in back there: to draw in fresh air (which then generally gets pushed into the cabin).

    Take a look at the Lancia Delta HF Integrale Evo II below. The front vent pulls air up through the radiatior; the rear vent pushes air down into the intake:
    great post^
    a couple of points on hood-vents:

    1) by evacuating air out of the engine bay (in theory anyway) you allow more air to come thru the radiator = better cooling
    2) even though the coolant/radiator and oil-cooler does most of the engine cooling, keeping the air in the engine bay cool has impact as well. The exhaust manifold is responsible for most of the heat in the engine bay and getting rid of that hot air can only help. Additional mods I did to my nose is to add breather openings that increase the exposure of the radiator and by opening a slot in the bumper increasing the exposure of the inter-cooler. All these mods including koyo large capacity radiator ...mean that I no longer have cooling issues at the track
    3) by flowing more air out of the engine bay down force should be increased and drag should be decreased

    you can see my front breather mods in the picture of my previous post

  13. #13
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    My motor's not set up for air cooling; no fins and the cylinders are wrapped in a metal jacket of cooling pipes. My working theory is, heat that negatively affects motor performance comes from inside my motor where the gasoline is exploding many times a second. I'm not trying to get manifold heat away from the motor, I'm trying to get air flow through my heat exchangers (and trying to keep manifold heat IN the manifolds to aid exhaust flow; that's why they're coated).

    Air flow across my heat exchangers takes high pressure on one side and low pressure on the other side; then air will flow from high to low.

    If I locate a hood vent somewhere in the engine compartment, I need to know what the pressure at that point is. I also need to know what the pressure on the hood side of that point is.

    I want to maximize pressure differentials across the heat exchangers. Getting rid of heat other places is desirable, but not if I have offsetting losses at my heat exchangers.

    I know I will have high pressure on the front side of the radiator/oil cooler. If I already have low pressure behind there, I won't necessarily create even lower pressure by putting a hood vent in that area, unless the pressure on top of the hood at that spot is even lower. Hood pressures tend to be low front, high rear, but absolute low-high isn't helpful; I need lower-than-low.

    Different configurations of front undertray can make a big difference in lowering pressure behind the radiator, even before I get to hood vents. Bigger tray isn't always better and shapes can make a difference too.

    If I have high pressure in the rear of the bay, I may have even higher pressure on the hood side there, and I'll just be dumping more air in if I add a vent.

    A small front lip spoiler might get rid of more air pressure in the rear of the bay than a hood vent could.

    For each car I just have to measure with the air pressure gauge and extension tubes, driving the car around and then doing some additional tests at the track to confirm what's going on at speeds on the straights. The digital gauges are cheap now, like $40 plus $5 for some flex tubing to run out to the measurement points (tape the end down at right angle to air flow).
    If God meant for man to motor-swap LS engines into track cars, He wouldn't have created Corvettes.

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  15. #15
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    If the MKAH Motorsports Hood Vents were not so expensive I would probably look at them closer.
    Last edited by peapodf50; 08-03-2017 at 06:24 PM.

  16. #16
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    i have just the center piece of this set. http://trackspecmotorsports.com/shop...od-louvers-kit

    but directing/forcing the air into your heat exchangers (oil cooler & radiator) is more important than venting the hood.
    always trying to make it lighter and faster

    ^^former build: http://www.bimmerforums.com/forum/sh...-neglected-M3/
    current build: http://forums.pelicanparts.com/porsc...car-build.html
    instant grams: doktor_b

  17. #17
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    I have an ideas for a vent. I was thinking that I could carefully cut the hood and bend down the fins to create airflow out of the hood. Anyone have experience with this?

  18. #18
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    Quote Originally Posted by peapodf50 View Post
    I have an ideas for a vent. I was thinking that I could carefully cut the hood and bend down the fins to create airflow out of the hood. Anyone have experience with this?
    go check mikestokeman's drift car thread as well as tptrsn's LRS thread. also in the drift subforum. they've both done that.
    always trying to make it lighter and faster

    ^^former build: http://www.bimmerforums.com/forum/sh...-neglected-M3/
    current build: http://forums.pelicanparts.com/porsc...car-build.html
    instant grams: doktor_b

  19. #19
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    kinetic edit.jpg I also bought a hvac return vent from home depot, cut it up into 4 strips and riveted it on. Used the blue vinyl to cover the rivets and edges of the vent.10533384_783172118406211_3222299436426130025_n.jpg
    Last edited by eye145; 08-09-2017 at 11:00 PM.

  20. #20
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    Here's an affordable option that looks great

    http://n15design.com/product/e36-coupe-hood-vents/

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